I never set out to tangle with the revered memory of Robert Stephen Hawker, vicar of the seacliff-bound parish of Morwenstow in north Cornwall from 1835-75. What I originally intended to do in The Wreck at Sharpnose Point was recount, as far as possible, the true story behind a singular ship's figurehead, which still stands in Morwenstow's remote and alluring graveyard.

But then I discovered that the maverick vicar had played a leading role in the aftermath of the shipwreck in question, including burying the dead, raising the figurehead over their grave and giving house room to the one survivor. Moreover, he had published his own detailed account of the wreck, and penned a poem on the subject as well.

My book was conceived, in one sense, as an experiment in historical retrieval; how much factual detail regarding a ship, her loss in 1842, and the lives of her crew remained available over 160 years later? And could those facts, however scarce, serve as the foundations for a creative dramatisation of the events leading up to and including the loss of the ship?

The Caledonia of Arbroath was wrecked at Sharpnose Point, Morwenstow, en route from Odessa to Gloucester with a cargo of grain. As the brig sailed up the north Cornwall coast on the stormy night of September 7 1842, she had nine crewmen on board, all but one of them from the immediate area of Arbroath. This and the subsequent "facts" - the ship's loss, the death and burial at Morwenstow of all her crew except the surviving outsider, a Jerseyman called Le Dain - were contained in Hawker's evocative article, which appeared in a Victorian periodical some 20 years after the events it described.

It soon became clear that my researches were not only taking me, as I had hoped, beyond Hawker's account, but were plainly contradicting him. Hawker, renowned for his services to the sea dead at a time when most people along this inaccessible coast were still regarded as wreckers to the core, claimed to have recovered and buried all eight drowned crewmen. But a cursory glance in the parish's burial register showed only five. Three were missing. I finally tracked two of them to unmarked graves in other coastal churchyards in Devon. The last, it seems, was never recovered; nor could I find any archive trace of him.

Hawker was notorious for never letting facts "stand in the way of his imagination", as one of his biographers conceded. But securing a Christian burial, as the only available solace to the bereaved, was truly a matter of life and death to the devout early Victorians. As such, this was a significant lie. At the very least, it raised suspicions about the reliability of the rest of Hawker's account.

These proved well founded, notably when Hawker took credit in his article for finding the survivor on the cliffs. My researches led me to a Dorset rectory, home of the descendant of a contemporary and one-time friend of Hawker called John Adams. He had scribbled exclamatory notes in the margin of his copy of Hawker's account, which remain in his descendant's possession. For one thing, Adams claimed it was he who had found the survivor, and his family who had cared for him. It subsequently transpired that Hawker and Adams had fallen out. There were allegations of unpaid debts, which Hawker had countered with accusations of poetic plagiarism. Adams published his own poetic version of the events of 1842.

It soon became clear that I could not tell the story of the Caledonia without including a considerable amount of detail on Hawker himself. I increasingly wondered how the Caledonia lies had served him. Hawker's letters and notebooks are littered with references to the sea dead. He constantly mentions the tally of sailors he buried, as many as 40 during his lifetime, and bemoaned the lack of recognition he received for this unpleasant duty. I began to wonder whether he might even have been hiding something more sinister; Morwenstow, after all, had been notorious for its merciless wreckers just a few decades before Hawker's arrival there.

Some people in north Cornwall and elsewhere feel I have done Hawker a disservice. I would argue that the question I have asked of him - why should a vicar repeatedly lie about the number of drowned sailors buried in his graveyard? - is a reasonable, even compelling one.

· Jeremy Seal is co-presenter of Wreck Detectives on Channel 4. The Wreck at Sharpnose Point is published by Picador at £7.99.